scd: Add option --clear to PASSWD.
* scd/command.c (cmd_passwd): Add option --clear. (send_status_printf): New. * scd/app-common.h (APP_CHANGE_FLAG_CLEAR): New. * scd/app-nks.c (do_change_pin): Return an error if that option is used. * scd/app-openpgp.c (do_change_pin): Ditto.
Card application may support this option to clear the PIN verification
status of a specific PIN.
(cherry picked from commit 29929e65521279eabc98a67c766fe485057405a9)
- Signed-off-by: Werner Koch <wk@gnupg.org>